Effect of parenteral cladribine on relapse rates in patients with relapsing forms of multiple sclerosis: results of a 2-year, double-blind, placebo-controlled, crossover study

Objective This randomized, 2-year, double-blind, placebo-controlled, crossover study evaluated cladribine for relapsing forms of multiple sclerosis. Design Patients (n = 84) received seven 5-day courses of subcutaneous cladribine at 5 mg/day (group A) or placebo (group B) in year 1; treatment was reversed in year 2. Results Cladribine was well tolerated and associated with a favorable safety profile. Mean Expanded Disability Status Scale scores remained stable. In group A, mean relapse rates were 0.15 in year 1 (cladribine) and 0.42 in year 2. In group B, relapse rates were 0.61 in year 1 and 0.50 in year 2 (cladribine). Patients required fewer steroid courses during cladribine periods. The therapeutic efficacy of cladribine was associated with a sustained reduction in lymphocyte count.